In recent years, use of organic Electro Luminescence (EL) panels that rely on the phenomenon of electroluminescence of organic material has been proposed for display panels used in display devices such as digital televisions. A matrix of red, green, and blue organic light-emitting elements is arranged in an organic EL panel.
It is important to improve light-extraction efficiency of the light-emitting elements, for example from the standpoint of reducing power consumption or increasing service life of the organic EL panel. To this end, Patent Literature 1 proposes technology for increasing light-extraction efficiency of an organic light-emitting element in which a reflecting anode, a transparent conductive layer, a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer, an electron injection layer, and a transparent cathode are layered on a substrate. Light-extraction efficiency is increased by using the phenomenon of interference between light that travels directly from the organic light-emitting layer towards the transparent cathode and light that reflects off the reflecting anode after being emitted from the organic light-emitting layer and then travels towards the transparent cathode. Specifically, Patent Literature 1 discloses that by setting the thickness of the transparent conductive layer (refractive index 2.2) to 183 nm, the thickness of the hole injection layer (refractive index 1.85) to 80 nm, and the thickness of the hole transport layer (refractive index 1.85) to 20 nm, the light-extraction efficiency of blue light at a wavelength of 470 nm increased from 2.0% to 3.0% (paragraphs 0043-0045).